字符串相等(==)的全测试

1. package p1;
3. /**
4.  * 字符串相等(==)的全测试。
5.  * 
6.  * @author XT Zang,老紫竹
7.  */
8. class TestString1 {
10.   public static void main(String[] args) {
12.     String hello = "Hello", lo = "lo";
14.     System.out.print((hello == "Hello") + " "); // true
16.     System.out.print((Other.hello == hello) + " "); // true
18.     System.out.print((p2.Other.hello == hello) + " "); // true
20.     System.out.print((hello == ("Hel" + "lo")) + " "); // true
22.     System.out.print((hello == ("Hel" + lo)) + " "); // false
24.     System.out.println(hello == ("Hel" + lo).intern()); // true
26.   }
28. }
30. class Other {
31.   static String hello = "Hello";
32. }

1. package p2;
3. public class Other {
4.   public static String hello = "Hello";
5. }

结论：

This example illustrates six points:

• Literal strings within the same class (§8) in the same package (§7) represent references to the same String object (§4.3.1).相同包，相同类的字符串常量指向相同的字符串对象
  

• Literal strings within different classes in the same package represent references to the same String object.相同包，不相同类的字符串常量指向相同的字符串对象

• Literal strings within different classes in different packages likewise represent references to the same String object.不同包，不同类的字符串常量指向相同的字符串对象

• Strings computed by constant expressions (§15.28) are computed at compile time and then treated as if they were literals.字符串在编译期间可以连接起来的，视同一个常量字符串

• Strings computed by concatenation at run time are newly created and therefore distinct.

The result of explicitly interning a computed string is the same string as any pre-existing literal string with the same contents.

参考地址：http://blog.youkuaiyun.com/ZangXT/archive/2008/10/11/3057471.aspx